1. Field of the Invention
The present invention relates to an angular velocity sensor used to correct camera shake and a method of setting temperature characteristics of the angular velocity sensor.
2. Description of the Related Art
In digital still cameras and digital video cameras, an angular velocity sensor arranged to detect camera shake is used to correct camera shake. Such an angular velocity sensor is driven by an oscillation circuit including a piezoelectric vibrator, detects a voltage caused by the vibrations of the piezoelectric vibrator that occur due to the Coriolis force, and outputs a voltage signal based on an angular velocity. The differential amplification of the voltage of the piezoelectric vibrator is performed. The synchronous detection of the differential amplification result is performed in synchronization with a driving signal driving the piezoelectric vibrator. The synchronous detection result is converted into a direct voltage signal. Direct-current amplification of the direct voltage signal is performed.
As the difference between the frequency of the voltage signal of the piezoelectric vibrator and the oscillation frequency of the oscillation circuit (hereinafter referred to as a “detuning frequency”) decreases, the detection sensitivity of an angular velocity increases. Since the detuning frequency has temperature characteristics, the detection sensitivity of an angular velocity changes in accordance with the temperature.
However, when the sensitivity of an angular velocity sensor changes in accordance with the temperature, even if the angular velocity sensor detects the same angular velocity, the detection result varies in accordance with the temperature. Accordingly, in known angular velocity sensors, sensitivity correction is performed so that the detection sensitivity of an angular velocity falls within a predetermined range over an operating temperature range.
Japanese Unexamined Patent Application Publication No. 11-344344 discloses an angular velocity sensor in which a temperature-sensitive element, such as a thermistor, is used as a resistor included in a phase-shift circuit which includes a capacitor and the resistor. Here, the configuration of the angular velocity sensor disclosed in Japanese Unexamined Patent Application Publication No. 11-344344 will be described with reference to FIG. 1. Referring to FIG. 1, electrodes 5, 7, and 9 of a cylindrical piezoelectric vibrator 10 are connected to a reference potential. Detection electrodes 6 and 8 are connected to a differential amplifier 11 and a phase-shift circuit 14. The phase-shift circuit 14 is connected to a driving electrode 4 of the piezoelectric vibrator 10 via a driving oscillation circuit 15, whereby a self-oscillation loop is provided. Consequently, an alternating voltage of a frequency that is substantially the same as the resonant frequency of the piezoelectric vibrator 10 is applied to the driving electrode 4, and bending vibrations are therefore excited in the X direction. Since the detection electrodes 6 and 8 are symmetric with respect to the bending vibrations in the X direction, the outputs of the X directional component are canceled out by the differential amplifier 11.
The outputs of the detection electrodes 6 and 8 have opposite phases with respect to the bending vibrations caused by the Coriolis force. Accordingly, only the Y directional component, that is, an alternating voltage proportional to a rotational angular velocity, is output from the differential amplifier 11. The synchronous detection of the output of the differential amplifier 11 is performed by a synchronous detection circuit 12. The synchronous detection result is rectified by a low-pass filter 13. Consequently, a direct voltage proportional to the rotational angular velocity is output to an output terminal 16.
In the above-described circuit, a temperature-sensitive element 19 is provided as a resistance element included in an RC circuit of the phase-shift circuit 14.
However, such an angular velocity sensor disclosed in Japanese Unexamined Patent Application Publication No. 11-344344 in which a circuit constant of a phase-shift circuit included in an oscillation loop of a driving oscillation circuit of a piezoelectric vibrator is corrected using a temperature-sensitive element requires, for example, a temperature-sensitive chip resistor for temperature compensation. It is therefore necessary to provide space for the temperature-sensitive chip resistor in the angular velocity sensor. However, for example, in a compact angular velocity sensor having an area substantially equal to or less than an area of about 4 mm×about 4 mm, the space for such a chip component is not available. In spite of its limited space, if the chip component is provided in the angular velocity sensor, the chip component must be surface mounted. In this case, the productivity of the angular velocity sensor is significantly decreased.